At present, a signal insulation method based on a photo-coupler has been widely used in systems requiring electrical insulation such as industrial equipment or medical equipment. However, it has become difficult in systems using photo-couplers to cope with recent high speed operations due to problems such as low data rate, duty ratio deterioration, etc. Therefore, the foregoing method has been replaced by an insulation method using a digital isolator that can solve these problems.
For example, an ADS board is used to control reactor-related AIO, DIO at a cycle of 50 msec. In an ADS board, a photo-coupler is used as an insulating element of DO. When a photo-coupler is used as an insulating element of Fast ADS developed for the purpose of further high-speed driving, a 50% duty ratio of DO cannot be obtained. Therefore, a digital isolator which enables the 50% duty ratio even under high speed driving can be adopted. The output side of the digital isolator may fall into an indefinite state in a power supply unstable state or the like at a power-on time, power cut-off time or the like. Such an indefinite state may impair reliability or safety.